ARM: properly lower dllimport'ed global values

This completes the handling for DLL import storage symbols when lowering
instructions.  A DLL import storage symbol must have an additional load
performed prior to use.  This is applicable to variables and functions.

This is particularly important for non-function symbols as it is possible to
handle function references by emitting a thunk which performs the translation
from the unprefixed __imp_ symbol to the proper symbol (although, this is a
non-optimal lowering).  For a variable symbol, no such thunk can be
accommodated.

llvm-svn: 212431

2 files changed, 84 insertions, 2 deletions

diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index f0fab69b66b..4bfa5a8b5c6 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -1654,6 +1654,19 @@ ARMTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
       assert(Subtarget->isTargetMachO() && "WrapperPIC use on non-MachO?");
       Callee = DAG.getNode(ARMISD::WrapperPIC, dl, getPointerTy(),
                            DAG.getTargetGlobalAddress(GV, dl, getPointerTy()));
+    } else if (Subtarget->isTargetCOFF()) {
+      assert(Subtarget->isTargetWindows() &&
+             "Windows is the only supported COFF target");
+      unsigned TargetFlags = GV->hasDLLImportStorageClass()
+                                 ? ARMII::MO_DLLIMPORT
+                                 : ARMII::MO_NO_FLAG;
+      Callee = DAG.getTargetGlobalAddress(GV, dl, getPointerTy(), /*Offset=*/0,
+                                          TargetFlags);
+      if (GV->hasDLLImportStorageClass())
+        Callee = DAG.getLoad(getPointerTy(), dl, DAG.getEntryNode(),
+                             DAG.getNode(ARMISD::Wrapper, dl, getPointerTy(),
+                                         Callee), MachinePointerInfo::getGOT(),
+                             false, false, false, 0);
     } else {
       // On ELF targets for PIC code, direct calls should go through the PLT
       unsigned OpFlags = 0;
@@ -2489,15 +2502,23 @@ SDValue ARMTargetLowering::LowerGlobalAddressWindows(SDValue Op,
          "Windows on ARM expects to use movw/movt");
 
   const GlobalValue *GV = cast<GlobalAddressSDNode>(Op)->getGlobal();
+  const ARMII::TOF TargetFlags =
+    (GV->hasDLLImportStorageClass() ? ARMII::MO_DLLIMPORT : ARMII::MO_NO_FLAG);
   EVT PtrVT = getPointerTy();
+  SDValue Result;
   SDLoc DL(Op);
 
   ++NumMovwMovt;
 
   // FIXME: Once remat is capable of dealing with instructions with register
   // operands, expand this into two nodes.
-  return DAG.getNode(ARMISD::Wrapper, DL, PtrVT,
-                     DAG.getTargetGlobalAddress(GV, DL, PtrVT));
+  Result = DAG.getNode(ARMISD::Wrapper, DL, PtrVT,
+                       DAG.getTargetGlobalAddress(GV, DL, PtrVT, /*Offset=*/0,
+                                                  TargetFlags));
+  if (GV->hasDLLImportStorageClass())
+    Result = DAG.getLoad(PtrVT, DL, DAG.getEntryNode(), Result,
+                         MachinePointerInfo::getGOT(), false, false, false, 0);
+  return Result;
 }
 
 SDValue ARMTargetLowering::LowerGLOBAL_OFFSET_TABLE(SDValue Op,
diff --git a/llvm/test/CodeGen/ARM/Windows/dllimport.ll b/llvm/test/CodeGen/ARM/Windows/dllimport.ll
new file mode 100644
index 00000000000..bc737bd4182
--- /dev/null
+++ b/llvm/test/CodeGen/ARM/Windows/dllimport.ll
@@ -0,0 +1,61 @@
+; RUN: llc -mtriple thumbv7-windows -filetype asm -o - %s | FileCheck %s
+
+; ModuleID = 'dllimport.c'
+
+@var = external dllimport global i32
+@ext = external global i32
+declare dllimport arm_aapcs_vfpcc i32 @external()
+declare arm_aapcs_vfpcc i32 @internal()
+
+define arm_aapcs_vfpcc i32 @get_var() {
+  %1 = load i32* @var, align 4
+  ret i32 %1
+}
+
+; CHECK-LABEL: get_var
+; CHECK: movw r0, :lower16:__imp_var
+; CHECK: movt r0, :upper16:__imp_var
+; CHECK: ldr r0, [r0]
+; CHECK: ldr r0, [r0]
+; CHECK: bx lr
+
+define arm_aapcs_vfpcc i32 @get_ext() {
+  %1 = load i32* @ext, align 4
+  ret i32 %1
+}
+
+; CHECK-LABEL: get_ext
+; CHECK: movw r0, :lower16:ext
+; CHECK: movt r0, :upper16:ext
+; CHECK: ldr r0, [r0]
+; CHECK: bx lr
+
+define arm_aapcs_vfpcc i32* @get_var_pointer() {
+  ret i32* @var
+}
+
+; CHECK-LABEL: get_var_pointer
+; CHECK:  movw r0, :lower16:__imp_var
+; CHECK:  movt r0, :upper16:__imp_var
+; CHECK:  ldr r0, [r0]
+; CHECK:  bx lr
+
+define arm_aapcs_vfpcc i32 @call_external() {
+  %call = tail call arm_aapcs_vfpcc i32 @external()
+  ret i32 %call
+}
+
+; CHECK-LABEL: call_external
+; CHECK: movw r0, :lower16:__imp_external
+; CHECK: movt r0, :upper16:__imp_external
+; CHECK: ldr r0, [r0]
+; CHECK: bx r0
+
+define arm_aapcs_vfpcc i32 @call_internal() {
+  %call = tail call arm_aapcs_vfpcc i32 @internal()
+  ret i32 %call
+}
+
+; CHECK-LABEL: call_internal
+; CHECK: b internal
+